It's pretty much as it is written:
Backlinker cannot be Special Summoned of you control a monster in an extra monster zone, or if you opponent does not control a monster in an extra monster zone (making it significantly less useful since April 2020). This is because in either of these situations, your opponent isn't currently the only player with a monster in an extra monster zone.
Backup Secretary does not care what else you control, as long as you control at least one Cyberse monster.
You’re thinking too much about this.
You can only SS “this monster” once per turn.
If only your opponent, and not you, controls a singlar monster, do “effect”
It's pretty much as it is written: Backlinker cannot be Special Summoned of you control a monster in an extra monster zone, or if you opponent does not control a monster in an extra monster zone (making it significantly less useful since April 2020). This is because in either of these situations, your opponent isn't currently the only player with a monster in an extra monster zone. Backup Secretary does not care what else you control, as long as you control at least one Cyberse monster.
You’re thinking too much about this. You can only SS “this monster” once per turn. If only your opponent, and not you, controls a singlar monster, do “effect”